Crude oil and any of their distillates, such as diesel, gasoil, naphtha and kerosene, contain different percentages of paraffins, which precipitate when the temperature decreases and crystallize very often coating the hydrocarbon.
The crystallization and agglomeration of paraffins degrade the flow properties of the oil or their distillates and break off the extraction procedure, processing, transport, storage and the use of the hydrocarbon.
This paraffin agglomeration is often observed during winter, when the environmental temperature falls and approaches to the pour point, producing the obstruction and even the complete plugging of pipelines in refineries, storage centers and other installations for petroleum processing.
Paraffin agglomeration takes place also in some crude distillates, in example diesel, producing obstructions in the filters of internal combustion motors, plugging heating pipes, which results in a bad operation.
When there is a cooling, paraffins disaggregate and form small crystals which interact forming a tridimensional network able to trap the liquid and increasing the viscosity. If this one happens in distillates like diesel, filter and valve stoppages are observed, but, when this phenomenon occurs in crude oil, the petroleum suffers gelling and deposits are formed on pipelines and storage tanks, provoking great damages to the production and storage capacity.
There are two kinds of flow improvers: nucleation and Crystal growing modifiers (Odriozola et al, 2008). The first promote the formation of tiny paraffin crystals, whereas the second kind facilitates the appearance of great crystal groups. In both cases the formation of a tridimensional crystal network is hindered. Nucleation modifiers are applied in gas and diesel transport and processing because paraffin crystals are so tiny that they can traverse trough filters. In contrast, growing modifiers are specially employed in crude oils (Tomassen H P M et al, 1998).
Most common flow modifiers are polymers, some of them homopolymers and the most copolymers. Homopolymers are obtained by reacting a single monomer while copolymers are synthesized from a combination of two different copolymers (M1 and M2). Monomers forming a copolymer chain may be arranged following an alternate sequence (alternate copolymer M1M2M1M2M1M2), or a succession of first monomers followed by a succession of the second monomer (block copolymers M1 M1 M1 M1 M2 M2 M2 M2) or a random sequence of monomers (M1 M2 M1 M1 M2 M2 M2 M1). This last kind of copolymers is specially characterized by their high homogeneous composition. The monomer sequence arrangement in copolymer chains, just that composition homogeneity, has a strong influence on their application properties. The use of single terpolymers as petroleum flow improvers has not yet been reported.
In the specific case of polymers employed as petroleum flow improvers, branched polyolefins, alphaolefin and esters of unsaturated carboxylic acids copolymers, ethylene and vinyl esters of fat acid copolymers, vinyl acetate and alpha olefin copolymers, styrene maleic anhydride copolymers, fatty acid amides and polyalkylacrylates, (Castro L V et al, 2008).
More specifically, ethylene-vinyl acetate copolymers (EVA) are produced by BASF under the trade mark Keroflux (Eisenbeis A et al., 2005).
Some examples of petroleum flow improvers given by the international literature are the following: European Patent No. EP0931825 B1 depicts a process for improving flow properties of oils with a sulfur content lower than 500 ppm and a minimal paraffin content around 8% by weight, using mixtures of copolymers and terpolymers, at a rate of 15% to 50% by weight of copolymers consisting of: polyethylene from 87% to 92% mol; polyvinyl acetate from 6.5% to 12% mol and 4-methyl-polypentene from 0.5% to 6% mol and terpolymers made of ethylene, vinyl esters and vinyl acrylates, at a composition between 50 and 85% (Krull M et al, 2003).
U.S. Pat. No. 4,362,533 describes the synthesis and use of terpolymers as pour point depressors for crude oil middle distillates, made of polyethylene (45-75% wt.), at least 5 by weight of polyvinyl acetate and 5% by weight of polystyrene. These polymers present a homogeneous distribution and composition of each monomer (Kidd, N. A., 1982).
European Patent No. 0136698A2 describes as a new flow improver a polymer with content between 50 and 90% by weight of ethylene, 10 to 40% by weight of esters of polyvinyl, 0.2 to 10% by weight of olefins and 2% to 25% by weight of aromatic vinyl, its molecular mass vary from 1,000 to 50,000, more preferably 2,000 to 10,000 Dalton. The polymer is added at concentrations between 0.03 and 0.10% by weight, being very effective to decrease the pour point of oils and middle distillates of petroleum (Chen J C S, 1985).
U.S. Patent Publication No. 2004/0092665 describes the use of copolymers constituted by a butylic fraction (isoprene, butadiene, 2,4-dimethyl-butadiene, 2,4-hexadiene and halogenated derivatives, among others) and styrenic fraction (alpha-methyl-styrene and styrene) (Pazur R et al, 2004).
Copolymer synthesized from vinyl esters, alkyl acrylate and styrene were added (200 to 4,000 ppm) into Mexican crude oils and diminished viscosity and pour point (Castro L V et al, 2008). These additives were synthesized by semi continuous emulsion polymerization and, afterwards, characterized by spectroscopic and calorimetric techniques, in order to ensure a random distribution in the chains and a homogeneous composition. The synthesis procedure showed their efficiency to avoid the formation of homopolymer mixtures. The performance of these products depends strongly on this molecular feature and on the absence of long sequences of a single monomer.
In Mexico, the reserves of light crude oil diminishes very fast and, in consequence, only heavy and extra-heavy crude oils will be processed in the future by the national system of refineries. This situation represents a challenge because of the technical and economical difficulties related to this problem. Therefore, it is very important to find a solution to the problem of the low API gravity and high viscosity of the Mexican crude oils (Camacho-Bragado et al, 2002).
Taking in account the great importance of these technical and economical requirements, a series of formulations of new random copolymers and terpolymers dissolved in different solvents was prepared. All these polymers were prepared by emulsion polymerization and showed a considerable performance as pour point and viscosity decrease agents in some Mexican crude oils. It is important to remark that none of the references mentioned above neither disclose nor claim the application of polymers and/or formulations whose main characteristic is that polymers are composed of combinations of two or three acrylic, vinylic and styrenic monomers together at random which main component are styrenic type.